Method of electrolysis



H. L. S'II'EWART 2,340,254

METHOD OF ELECTROLYSIS Jan. 25, 1944.

5 Sheets-Shed 1 Filed Jan. 17, 1939 Jan. 25, 1944. H. L. STEWART METHOD OF ELECTROLYSIS Filed Jan. 17, 1939 5 Sheets-Sheet 4 r I Jan. 25, 1944. STEWART 2,340,254

METHOD OF ELECTROLYSIS Filed Jan. 17, 1939 5 Sheets-Sheet 5 v F914. 10 as m 110 m through its end portion shown denote similarpartsin the.

rsmiefdi snrze f y umen Hubert nsm'mmbmm rs..- mm; to Koppel: Company,.rittshnrxhplta a-corporar tion ame-i January 1'1, 19:9. sensin 51.41;

.Thisinvention use. to improvements in. ap-

paratueicr'electrolyaisandmethodsfoi 'operatine the same. Moreparticularlytheinrention relates-to improvementsi-in'the electrolytic preparationofchemicals from. solutions of electrolytes.

Apparatus toruse inthe present invention are illustrated by way oi'example in theaccomp'anying:.drawinIs-in which: v I v Figure 1 illustrates apparatus in a 7 system. for

operatinaan electrolytic-cell for the preparation.

otchemicals:

2. is. a longitudinal substantially cen re! sectional-view or; a cell unitior in'thelabove 3-is-a. sectional riewoi -the cell on line} in.Fi:.-.2 inthedirectionog the arrows;

Figs; 4 anddiare traamentary vie'wrol the cell shewnin Has. 2 audit;

. a valve I leads into the top or thetanlt. A'pipe I havingv a valve-8' leads. from adjacent the desirable; A p L lutionvisirepeatedly; through the ceii 'ata regulated rate. Y'rhe cellfisequipped to'pe'rmit continuous passage 0! electrolyte solution there v through.

I'The. tank Imay open atjthe tcp'and maybe provided withaconical bo'ttom with an outlet-pipe Shaving avalve 4. A reed; pipe?! provided with tom. oi. the tank! to a. pump 9; The. .pipe'l may have a portion II that 'xtendsiintofthertank; 2

T normal level-oi the liquid maintained 'in"the tank: The pressure side; f'the pump 9 1s connected by; a pipe" toan indirect heatexchangeimeans:1 3

in: fluid the-flow of whichisconttolle'dfby wal ves and 11.. A pipe; "leads tram. the'heat-exchanger ll-to a .fllter- It; A fl'lterofgthetype. I shown in Figs. 115 and 18 and descnbedin-detail, belowmaybeempioyed- Apipeioior thefiltrateri -14 isian end'iiew or the said improved 7 means on. the end or. thecellshown in Fig. l2;

Biz. i5. is a vertical sectional jview of aI-fllter empioyeein-thesystemsnowninm. 1; and

Fig. 16 is asectional. view 01 the Ifllter online lt-ll-oi'flmli in .the direction or the arrows.

liihecharacters diretei'en'ce are Lmploiedfto v several views. 1 1 In" 1. numeral idesienates anelectr'o;

' tytic cell having; appropriate electrical connec An'y suitahlertype-otcell may be employed.

:but in the electrolysis or sodium carbonate solution, for instance, to prepare sodium hydroxide and sodium bicarbonate, it. has been found. distinctl advantageous-to usegacell oi the type haw ct suchcell will-be descrihedin detailbelow.

Artank. or reservoir 2. is. provided irom which solution. to be electrolyzed is red to theeell. I,

and-to which elt ml'ymd solutionisy passed from the eel. Fortheelectrolysis a: an electrolyte solution such as sodium carhonatefsolution' :a cyclic possible by the iuse oi. the

.rate'oii Thepipes "fi d 24- areilshown'connectedto" V nected to the catholyte chamber or thejcelllfior in; a horizontal diaphragm. A preferred iorm' v andthatihas its cpen end H positioned- -below'the havingiinlet'iand outlet pipes Hand lt ior heatleadsirom the fllterto the-cell I; Valve "injthe' pipe "may herused' to -controi thewpassase-of liquldto thefllterr It. A pipe '22 havingvzavaivle It and connecting ass-hm.

' Apipegll'provided with a va-lve i l'connectsthe cell ito the tank'i. U H is positioned 'preierably below the leveloi; the liquid in the tank circulation or the. cooling. fluid:

theanobte'chamber'of the 'c'el l.*f' A'pipe 29156011- 7 e withdrawal or catholytes'olution; I in the use or a cellhaving ahorizontal di'a hrazm as distinguishedifromi aicell otlthefllterpress type provisicnzmay' hematit thS- resu' lation. o: the me of. passa e: orithe electrolyte through the poresin. the horizontaldiaphrazm or the cell by means oi apparatus ior-re'aulatina the diflerehtial pressure of the. sa'sesgenerated' at the cath0de" and: at the .anode: For this purpose'mea'ns may be.

the gasin the anolyte chaniberor the pressurefo! .the zasln the catholyte-chamberor-botmdependin: on" the desired-rate .cfflow otithe electrolyte through-the diaphrasm. v An example of the abovere'gulating means is shown-in Fla. 1'. A pipe apparatus to be described is minute be high]; a tone. in the lyte'chambefoi the cell I to. a

Riven portion; of. the electrolyte so pipes ii and 20-, serve;

An open e'nd oi theipipe I! andpadjacent'a 0001111812011 20 havinr'a'valvel'l at its lhl'etndfand" a valve ,2 at its outlet, end. for controllingmg provided tor, thefwithdra'wal of asesa'nd for adjusting ei'ther'the pressurejof 30 connects the gas" chamber oi communicating with the tank 2"by means of a pipe 32. A pipe 22 communicating with the gas zone in the x the cell I leads toa chamber 14 that communicates with-the tank 2 by means of a pipe 25. Liquid from the tank 2 passesinto the chambers 2i and 24 and the level Jfifiaiih assumes the same position as the level in theta; k 'l he ends of the pipes 20 and areprovided'iwith extensible sections 38 and'fl respectively, joints ior'which are gas tight. The positionofthe .open ends of the e; 'sions V of the liquid in the chambergil and respectively may thereby be varied and set to give desired predetermined pressure dlflerential which is indicated by a diflerential pressure gauge 22. One armroi the gauge is connected to the gas zone in the anolyte chamber of the'cell I by a pipe 29, and the other arm islconnected to the gas zone in the catholyte chamber by a pipe 40. The pressure in having ,a horizontal diaphragm may be main-' "-tain'edslightly' higher than the pressure in the catholyte chamber'by, positioning the free open end of the pipe 26, agreater distance below the level of the liquid than the free open end 01 the pipe-21. {The anode chamber! pressure may be the cathode chamber pressure attimes. Extensiblecpipesffl and 21 serve to change the a relative pressures consistent with proper feed.

the operation of .the apparatus shown in Fig. 1; sodium carbonate solution, for. instance, ispassed into the'tank 2 through the pipe" i and withdrawn from the catholytechamber of e I6 and 21 with respect to the level the anolyte chamber of a cell 7 the leveljoi the liquid is maintainedabove the I 1 cooling coil'28and abovethe'open end II oi the Pipe ll Y The carbonate solution is withdrawn .throiighithe pipe I II and then through the ;pipe

- I by. the pump I. The solution then flows the heater I3 where itfmay be heated to apredetermined temperature of irom about 60C. to about 80 C. before conducting it intothe anolyte chamber of the call I. solution is passed into the cell and electrolyzed to i'oim sodiumhydroxide in the catholyte chamher-g and sodium bicarbonate in th 8 13??? chamber.'. a The carbonate'solution is passed into the cell continuously through the pipe 22 and the anolyte andfcatholyte solutions are withdrawn from, the cell continuously through the pipes 2l1and 2 9- feed and withdrawal to; and Y iroxnthe anolyte chamber may be intermittent respectively. The

.' when desired, .The valves 21 or 22 may serve Jto resulatefthe feed to the cell. .The valve :5 in mar ne rsm to resi ate anolyte; solutioniirom theQcell. Recycling of e anolytesolutionlthrough a"cell may becaruhtilasatisiac concentration 01: bicarbonate fissiobteined inpthe anolytegsolution Therate of passage'oicarbonate solution through a cell diaphragr'nmaytberegul ted so as to obtain a sub fistantial'concentration of sodium hydroxide in the fcatholyte solution; Concentrations of sodiumi'hydroxide'ilup to-about 25% maybe obtainedi The system may be regulated to obtain a preferred/range;oihydroxide of about 11%.jto

about 18 Rangesot concentration of hydrozide'abovei25 %1 are'apt-to result in 'caking .outfoijsolid' caustic on the cathode.

' ezcatholyte solution from the cell withdrawn need notibe. recycled through "through thepipe 28 tliecell. 'In theuse is iormedin the pipe 22 to prevent escape of gas along 'with the catholyte solution. any gases through The heated carbonate the withdrawal oi a'horizontal'cell, a trap hydrogen from the catholyte and oxygen from the anolyte chambers are obtained as valuable by-products.

The anolyte solution obtained by electrolyzing sodium carbonate solution and containing in the early stages of the cyclic operation sodium bicarbonate and substantial proportions of unconverted sodium carbonate, passes to the tank 2 from thecell I and is returned to the cell through the heater I3. Heating of the liquid passing to the cell tends to maintain the bicarbonate in solution and. also tends to prevent convection currents in the cell. If desired, the tank 2 may be kept cooler. than the cell to permit crystallization of sodium bicarbonate in the tank.. For this-purpose thecooling coil 26 may be used to cool the solution in the tank 2. 7 Since bicarbonate has a lower solubility than carbonate, a saturated solution of the bicarbonate at a giventempera- -ture is obtained before-a saturated solution of bottom of the tank 2 and maybe withdrawn through the valve 4 and-passed into collectors.

Byway of example, a desirable range of concentration of the sodium carbonate solution initially introduced in the system may be about 1 pounds'to about 2 pounds per gallon'of water. With the use of asolution 0! such concentration the temperature may be brought down in the tank 2 within-the approximate range of 25 C. to 28 'C.- The temperature in tank 2 may however be higher or lower'tban this range. The concentration of the bicarbonate in the" system may in fact be controlled bycontrolling the degree of cooling in the tank 2., The;1ower the temperature below the point of saturation the more bicarbonate will separate Thesystem can be operated without cooling g thjellquid in the tank 1. 'In this case the liquid l initheientire circulatory system may be maint-tainedl-hot or at a predetermined temperature of; around to 80 C., and after a period of circulation the anolyte solution'containing the bicarbonate can ,be' cooled" outside-the cell to causej crystallization and separation of the bi- J use in the'formot a slurry.

carbonate in solid form. The solid bicarbonate may be separated from the motlier liquor by filtration orsettling, or itmaybe' produced for Liquid drawn from the tank'2 lorrecycling is preferably taken from near the'liquid level and its rate oitravel to and from the cell I maybe regulated by the valves land 25 respectively.

Sodiumcarbonate solution" may be added to the system through a pipe having a valve 44 and connected to the pipe I, or through the pipe] to maintain a constant level of liquid in the tank 2' and'to keep the sodium concentration substantially the same in the solution delivered to the cell." 7 The solution level in the anolyte chamber of the cell l may be regulated during the recycling process by means of a swing-joint 45 in the pipe 24.: The swing joint comprises a short pipe connection inserted in the pipe 2!, each end of which is connected by a swivel Joint which perraising and lowering of vthe end ll toa anolyte and catholyte clinic 3 of the pipe 24 that is connected to the'cell I."

The liquid in the tank 2 may, when desired,

be kept agitated. For {this purpose apump 46 maybe provided havingits intake connected to the pipe 'l-and its" pressure side connected to the top of the tank .2 by means of a pipe- 41. The discharge end of the pipe- 41 is preferably positioned at the solution level' and enterson a tangent whereby a swirling motion of the liquid results during pumping. Recycling of the solution through the tank-2 may be conducted simultaneously with the recycling of the solu-' tion through the cell I.

It is noted that a continuous cyclic means may be provided in the apparatus shown in Fig.

I. By -this is meant that the. said means make it possible to maintain liquid-in 'thecycle in a substantially unbroken stream.- 'The cycle. may be maintained while electrolysis products are removed and while fresh electrolyte is added, and also, as in the horizontal typeof cell,while any desired pressure-diiferential'is maintained BI and a cathodechamber 52. One important feature, of the cell is the arrangement thereinof the electrode surfaces, particularly ofthe' anode,

2,340,254 predetermined position above or below the end" hole 60. Washers i5 and 8t areprovided under r the nuts 82 and 83 respectively.-

The: anode of the cell comprises a plurality oi' metal-bars or Jslats 61 spaced a relatively short:

distance apart and extending .from oneside'of I the anode chamber 51 to the other, adjacent the diaphragmifl. Each of. the bars 67 comprises preferably aflat steel rod or. strip of ;a-rectangu:-;

la'r section (as shown in Fig. 2) and tilted'torslope downwardly from its upperedge 88 wits lower edge 69. in the direction of flow of the electrolyte soiutioninthe anode chamber The entrances,

for the electrolyte solution being at IO-and II,

and the outlet for the anolyte solution being at; t

12, the bars 61 slope downwardly toward-the exit 12. 'A fragmentary view of the anode frame looking upwardly from the-diaphragm is shown in Fig. 6. The-lower edges 88 of the. bars 81 are preferably flush with thelower edge of the frame 58 from which the flange '585extends. The upper edges 8801? the bars 61 may-bebelowthe level of the entrances Ill and II andoutlets l2, and are preferably below the level 13 of electrolyte solution maintained in the anolyte chamber I l. Thelupper edgesi68, of the bars 6.1, at theends thereof are welded to and abut againstsidebars 14' and "I5 welded to opposite sides-oftheyframe 53. The'middle *portion of eachbar 61 abuts against and is'welded toa bar 16 extending through the center'of the anoiytech'amberfromi,

one end thereof to the other. The bar 18 is welde.

whereby means are provided for efficiently" assisting in properly; directing flow of the electrolyte solution and of the products of ele'ctr'oly sis. Theconstruction and operation of this and other improved means will be'speciflcally de-' scribed below. a a

fftectangular "frames 53 and 54, preferably shallow, serve to enclose the anode and cathode compartments respectively. The sides and ends of. thejframes 53"" and 54 are constructed' from ed 'to' spaced blocks 11 whichare. in turn welded to the top of the cell..

The bars 61 are tilted-forv the purpose-1 of d8;

fleeting the electrolyte solution toward the diaphragm 50, as it flows through the anolyte chamher. A desirable. angle-oftiitis substantially thirty degrees to the horizontal.

The lastcross bar 81 :in theanolyte chamber 5| nearest the outlet 12 is preferably vertical and is spaced sufficiently from'the framewall to per-.

steel L'bars. The L bars inthe' framejSSare welded to thetop 55, and those in the frame 54 to the bottom 56 of the cell. The barsfare tilted so thatfthe flangeil formed by the bars'in the sides of the lower frame 54 slope downwardly away from thecellat an angle of about three.

degrees to. the diaphragm 50. .The flange formed Qbyfth'e L bars in the sides. of the upper frame t3 slope upwardly away from jthe cellf at. e ians e wihr e se I .F

ream. The rpqsaof this construction; is to' make possible'a tighter. seal between the frames.

The bottom frame is aflittlelarger; than. the

top frame so that when the frames are bolted together, the inner edge of the flange 51 eflects 58.: The flange 58 overlapsthe' diaphragm and assists inholding the edges thereof in place.

This arrangementfurthermore provides a oughly leak-proof joint.

thor

'Bolt holes 59 and to (plan views Figs. 4 and s),

spaced a relatively short distance. apart, are provided" in the flanges 51 and 58. respectively, for boltsi 6| screw-threaded at one or both ends. Nuts 62 and 63 onthe bolts 8l serve to clamp the flanges tightly together. The bolts are insulated from one orthe other of the flanges in any suit able manner as by means of a combined ring and gasket '84 fitting around the bolt and'in the bolt a gripping .action on the, surface of the flange.

' ing from side to side of the frame-54,;

mitflushing of the diaphragm surface... i The'cac-hode of the cell comprises a plurality of spaced metal rods orslats of rectangular section in the catholyte chamber 52 and. extend- 80 are supported-in a verticafposition with the lower edge 8| of-each resting at theends on side bars Hand 83 and welded thereto; The 'cen tral portion-of each rod 80 rests'on a'center bar J 84 extending through the center of thelcatholyte chamber from one end thereof to the'other. Thel center bar 84 is welded to a plurality of spaced blocks" and is supported thereby'above the bottom 56 crime cell. The upper'edge 880i each'rod 80 is preferably 'positioned slightlybelowithe'upper 'edge of the frame thus providing space for a diaphragm between the anode bars Gland the cathode bars 80." :Spacers fll'and'fl are provided between the bars SOVAfrag'mentary plan view of the cathode frameis shown in Fig. '4. "A pair of terminals passes throughthe-top 55 of the cell and is welded to" the .center bar ll;

A pair of terminals 8| passes throughthe bottom 56 of the' cell and is welded to-the center bar 84.

The terminals Slland 8ll are placed so as to obe tainuniform current distribution and are connected to the positive and negative terminals'respectively of a current source. I

"Conduits 82 and 93 are'connected to the anolyte i andcatholyte chambers BI and ilrespectively.

Connections such as fpipes:39 and 29 shown in Fig."

1 may be made'tothese conduits for the purpose indicated. above.

Various means made of compressible, corrosion The rods assembled.

' g resistant insulating: material may be employed for com ressing the diaphragm it and for holding the iatter'in place while the cell is in operation.

Referring to Fig. 5-, a rubber sheet oralkali-resisting insulating means having a border 94 which serves as a gasket between the flanges l1 and i8,

- makes it possible to have a thoroughlyleak-proof cell. Furthermore the border 94 serves as insulation between the flanges 51 and 58. V or ribs ll between the slots I lie crosswise of the cathode and anode bars" and 61: respective] and are pressed; downwardlyagainst the dia- I. by the lower edges 89 of the bars 81. The perforations 80' are for the passage therethrough of the bolts ll. It is: possible to pro.- vide -perforations in the sheet in'place of slots II, but an objection to perforations is that they causeclogging due to eddy currentsin the electrolyte as it passes through the cell;

' Another form of diaphragmcompressor means isshown in Figs. '1 and 8. Strips of rubber 98 or alkali-resisting material ofrelatively small width; and a thicknesssubstantially that ofthe- 7 distance between'the tiltedbars 81 in theanode,

are curled'around the lower edge of each bar (as asses The strips for a cell oi: the described above whereby flushing of .theilatter is made relatively simple and efllcient :The discharge end of the anolyte chamber 7 I "through which an electrolyte solution is conducted-,is'provided with a rectangular port in inthesend wall m r the said cham her and extending substantially across the width of the cell. discharge hood I08, comprising side wallslll! and III, a top Ill and bottom. 2' projecting from the port I and each convergingtoward a,.relatively small end-wall H1, is welded to the end of the cell. The bottom it! of the hood mayrest on the flange ill on the anode frame. Alongxthe portionof the flange Ill coyered by the' hood III, stud bolts I ll pass upwardly through the flange ill on the cathode frame andarethreaded into the flan e I. An insulation member I i'l insulates the bolti II from the flange I ISL"... Bolts I lijmay-be. spaced the same .7

distance, apart'ias the other bolts H8 along other portions-o! the; frames. r

An outlet pipe lllis provided in the-end-wall H3 of the .hood l. This pipe corresponds to the pipe-l2 (Fig. 2). .When used in the system shown in Fig. l the pipe .i "may be connected to the pipe .by means ofa swing-Joint 45.

-As shown inFig'. 13 when using the compression strips "onthe anode bars 81 an insulating gasketlll fltting'between the frames may be emindicated inFig. 7), the ends of a'strip being in-- Y serted in adjacent spaces'between the. bars 6].

The strips maybe'distributed as indicated in Fig..

8, which shows a portion of the anode looking upwardlyfrom the surface of the diaphragm when the cell tparts are assembled. In other words,

the strips areplaced in: alignment from one-end of. the cell to the other-in a, plurality of rows which rows are :spaced. at relativelyshort dis.- tanceapart, In alternate rows,=R1 and R: for.

instance,'the strips are placed onalternate bars;

a,-b, c, d, e; etc; In intermediate rows such as- Rs, the stripsare placed on alternate bars a, b, c, d, e, if, etc. With the strips in position the lower curved surface of each strip presses against By means of the strip it is possible to have activeabout 50% more of the surface of- .the

bars 01 than inthe arrangement shown in Fig.

.1 v,Various means maybe employed to serve Each anode bar is thereployed. The gasket may be made of rubber or the like, or other substance, preierably unailect; ed by alkaline-solutions; v The filter that may be employedin' the cyclic system shown in Fig. 1 anddesignated by the nu meral I! may-.be'constructed as shown in Figs. 15 and 16. By using two filters. one may be in use while the other is being cleaned. The filter shown. comprises an outer casing I25, preferably cylindrical, having an: inlet I18 adjacent one end and outlet I21 at or adjacent the-other end. ,An inspection plate 1 "is provided adjacent theinlet l2. Concentric with-the. casing 125 and with the outlet iflfisla perforated pipe I29 extending from the outlet e'nd of the casing. .125 to a'relatively shortsdistance from the inlet end. -The pipe I" is provided witha dead end I30- Concentric with the pipe I20, and of substantially the same length,'is a cylindrical screen I31. which is reinforced by means of ribs I32. The space ill between the screen III "and the pipe I2! is filled with afiltering medium'which may be any suitable granular or porous material. A satisfactory medium comprises two-"partsof sand and one part of asbestos fiber. This type'of filter per as-a diaphragm in the cell. A preferred form is shown in BigJ in which the two-layers of matted :as-

bestosror preferably of asbestos paper iii are placed between'two iayersofwoven asbestos or of asbestos'cloth I02. In Fig. 10, a form of diaphragm isshown with oneilayer of:asbestos paper VIII between two vlayers of asbestos cloth I02, In. Fig. 11,-;a form of diaphragm is shown in which the layers of fibrous material shown in Fig. 9 are placed on awire screen I03 of about 8 mesh. If desired, the diaphragm shown in Flg. '10 may similarly lie-mounted on a wire screen which when mounted in the. cell, rests on-the cathode; bars II. The diaphragm and other means between the electrodes. are-clamped vbetwe'enthe lower edges of the bars 61 and the up- 7 rm. :2. 1s and r4 illustrate atta hment means 7 edges of the bars "when the cell partsare mits continuous passage'zot liquid-therethrough. It is rugged enough to withstand the-eflects or plant usage: It can be readily'cleaned by blow ing live steamthrough it.

Inthe operation'of-the cell shown in Figs.l2 -'-6. the liquid to be electrolyzed flows into one end of the anolytechamberl il, as for instance, through the inlets I0 and H. A continuous flow :of liquid is preferably maintained throughthe anolyte chamber. Theflow may, however. be intermittent, as indicated. As'the liquid, brought to a level above the bars 61, proceeds towards the outlet 12 it isidefiected toward the diaphragm 50'. Theelectrolyte solution passes throughthe pores of the diaphragm. and downwardly between the bars 80. The rubber compressor means 81 (or II, Fig. 13) insure intimate contact between the cathode bars and the diaphragm "which becomes saturated with, and is maintained in constant contact with the.electrolyte s"olution during the passage of current through the cell;

Gas from the anolyte chamber is withdrawn through the pipe 92. Gas generated at the cathode, and the catholyte solution flow from the cell through the pipe 93 and are permitted to separate. The gases may be used to eilect a differential pressure on the diaphragm as described above.

A current density of about 0.40 to about 0.75 ampere per square inch may be employed in the electrolysis of sodium carbonate solution. Cells may be operated with about 200 to about 5000 amperes. A desirable current density has been found to be about 0.65 ampere per square inch; a desirable cell current is about 1000 amperes. A plurality of cells may be connected in series.

In providing the inclined anode bars 6'! a sumcient number thereof is used'in a cell to direct the flow of electrolyte properly therethrough as in a plurality of streams and to obtain uniform current distribution, and uniform contact of the electrolyte with the electrode. By properly tilting the anode bars, the formation of eddy currents in the flow of the electrolyte solution is diminished or substantially eliminated.

Other solutions besides sodium carbonate solution, namely potassium carbonate and sodium sulphate are effectively electrolyzed in the above cell and are suitable for treatment in the recycling apparatus shown in Fig. 1.

Reference is made herein to application Serial No. 87,569, filed June 26, 1936.

I claim:

1. An electrolytic process, comprising continuously and repeatedly-circulating a solution of alkali metal carbonate, at substantially the temperature range of about 60 C. to about 80 C., through the anolyte chamber of an electrolytic diaphragm cell, said temperature being employed for maintaining in solution alkali metal bicarbonate electrolytically produced in the anolyte chamber, and while withdrawing from said latter chamber the resultant solution containing said electrolytically produced completely dissolved alkali metal bicarbonate and unconverted alkali metal carbonate subjecting the anolyte chamber and catholyte chamber to controlled differential pressure by means 01' separately entrapped gases from said chambers thereby effecting passage of some of the anolyte solution through the diaphragm and generating alkali metal hydroxide solution in the catholyte chamber of the cell to concentrations up to about 25% thereby avoiding caking out of solid caustic on the cathode, and in the course of said process separately withdrawing from the'cell so-i'ormed solution containing the alkali metal. hydroxide, lowering the temperature of withdrawn solution containing alkali metal bicarbonate and alkali metal carbonate to effect solidification of alkali metal bicarbonate while maintaining the alkali metal carbonate in solution, and returning the alkali metal carbonate solution to the anolyte chamber of the cell for generation of additional alkali metal bicarbonate and alkali metal hydroxide.

2. An electrolytic process, comprising continuously and repeatedly circulating a solution of sodium carbonate, at substantially-the temperature range of about C. to about C., through the anolyte chamber of an electrolytic diaphragm cell, said temperature being employed for maintaining in solution sodium bicarbonate electrolytically produced in the anolyte chamber, and while withdrawing from said latter chamber the resultant solution containing said electrolytically produced completely dissolved sodium bicarbonate and unconverted sodium carbonate subjecting the anolyte chamber and catholyte chamber to controlled difierential pressure by means of separately entrapped gases from said chambers thereby effecting passage of some of the anolyte solution through the diaphragm and generating sodium hydroxide solution in the catholyte chamber of the cell to concentrations up to about 25% thereby avoiding caking out 0! solid caustic on the cathode, and in the course of said process separately withdrawing from the cell so-i'ormed solution containing the sodium hydroxide, lowering the temperature of withdrawn solution containing sodium bicarbonate and sodium carbonate to effect solidification of sodium bicarbonate while maintaining the sodium carbonate in solution, and returning the sodium carbonate solution to the anolyte chamber of the cell for generation of additional sodium bicarbonate and sodium hydroxide.

w H. L. STEWART. 

